A fuel cell is an apparatus which produces electrochemical reaction at the membrane electrode assembly (hereinafter, refer to as “MEA”.) comprising: an electrolyte layer (hereinafter, refer to as “electrolyte membrane”.); and electrodes (an anode catalyst layer and a cathode catalyst layer) being disposed on each surface of the electrolyte membrane to take the electric energy generated by the electrochemical reaction out from the MEA. Among the fuel cells, a solid polymer electrolyte fuel cell (hereinafter, refer to as “PEFC”.) used for, e.g., household cogeneration system and automobiles can be operated in a low temperature region. Because of high energy conversion efficiency, short start-up time, and small-sized and lightweight system, the PEFC has attracted attention as a power source of battery car or a portable power supply.
A unit cell of the PEFC comprises an MEA and a pair of current collectors (separators) sandwiching a laminated body including the MEA, wherein the MEA contains a proton-conducting polymer which exhibits proton conductivity. When operating the PEFC, a hydrogen-based gas (hereinafter, refer to as “hydrogen”.) is supplied to the anode and an oxygen-based gas (hereinafter, refer to as “air”.) is supplied to the cathode. The hydrogen supplied to the anode breaks down into a proton and an electron under action of catalyst contained in the anode catalyst layer; the proton derived from the hydrogen reaches the cathode catalyst layer through the anode catalyst layer and the electrolyte membrane. On the other hand, the electron reaches the cathode catalyst layer through an external circuit; by these processes, it is capable of taking the electric energy out. Meanwhile, the protons and electrons both having reached the cathode catalyst layer react with the oxygen contained in the air supplied to the cathode catalyst layer under action of catalyst contained in the cathode catalyst layer to produce water.
By keeping a proton-conducting polymer contained in the MEA in moisture state, it is possible to reduce proton conductivity resistance. So, when operating the PEFC, a humidified hydrogen and a humidified air (hereinafter, these may be summed up as “reaction gas”.) are supplied to the unit cell to keep the MEA in moisture state. However, the water existing in the unit cell can move together with the reaction gas towards the flow direction of the reaction gas. Therefore, within the MEA, mal-distribution of water may be caused. Specifically, an MEA region facing the upstream of the reaction-gas flow direction tends to be dried compared with other MEA regions facing the downstream of the reaction-gas flow direction. At the downstream of the reaction-gas flow direction, liquid water tends to be pooled and the pooled water often causes flooding. When the MEA is dried, proton conductivity resistance increases which results in decrease in PEFC's electricity generating performance. In addition, once flooding is caused, diffusion of reaction gas is inhibited, which results in decrease in frequency of occurrence of electrochemical reaction; thereby PEFC's electricity generating performance is decreased. Hence, to improve PEFC's electricity generating performance, it is necessary to inhibit occurrence of desiccation and flooding of the MEA.
Conventionally, as an art to inhibit flooding, a PEFC having reaction-gas flow passage of which inlet passage or outlet passage is blocked (hereinafter, refer to as “blocked passage”.) has been developed. By the mode having the blocked passage, it becomes possible to diffuse a large amount of reaction gas at regions of the laminated body facing a site of separator (hereinafter, refer to as “projection portion”.) located between neighboring passages. Thus, this mode of the PEFC makes it possible to improve its drainage.
For example, Patent document 1 discloses an art relating to a PEFC having a blocked passage.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 11-016591